I don't know what it's worth, but in "The Master Handbook of Acoustics" page 400 it says that small rooms become really problematic from 1,500 cubic feet or about 42 cubic meters.
"Room Size
Problems are inevitable if sound is recorded or reproduced in spaces that
are too small. Gilford1 states that studio volumes less than approximately
1,500 cu ft are so prone to sound coloration that they are impractical.
Rooms smaller than this produce sparse modal frequencies with exaggerated
spacings, which are the source of audible distortions."